As is well known, the inlet of a missile and the like is extremely critical and has a significant influence on the range, thrust level and maneuver capability of the vehicle. One significant contribution to inlets of supersonic missiles was the development of educated slots.
An educated throat bleed system is a passive throat bleed bypass arrangement which can enhance the stability of ramjet inlets. An educated bleed slot is one which passes only small amounts of bleed flow with supersonic approach Mach numbers (inlet supercritical) while maintaining approximately the higher bleed airflow characteristics of a plain slot when the flow over the slot is subsonic (inlet critical or subcritical). This provides a high ratio of critical-to-supercritical bleed airflow. This is accomplished by recessing the downstream lip of the bleed slot so that a large amount of the supersonic flow which expands around the bleed opening is turned back into the inlet. With subsonic flow approaching the bleed slot, the amount of flow bled is relatively unaffected by the fact that the lip is recessed.
An appropriate educated bleed slot design limits the supercritical inlet bleed flow (equivalent to that at pseudo-critical inlet operation) to that just required for boundary layer removal while providing for much larger amounts of bleed flow when external or internal flow perturbations suddenly push the inlet operation to near-critical, thus providing a bleed stability system.
The advantages and disadvantages of fixed and variable-geometry inlets have long been recognized. In favor of fixed-geometry inlets is its simplicity while variable-geometry inlets generally consist of a number of moving ramps contributing to its complexity with a consequential increase in weight.
I have found that I can improve overall performance of a two-dimensional inlet for a ramjet missile by providing variable geometry by a single ramp operating in combination with an educated slot. The single ramp is hinged at its aft end and unattached at its leading edge which is judiciously located relative to an educated slot bleed system.
The use of a single ramp in the educated slot configuration provides a more simple means for obtaining variable internal flow contraction and variable bleed area, thus making the variable-geometry inlet potentially more attractive than the fixed-geometry inlet for some applications. In this configuration the external-compression part of the inlet remains fixed.